694 



CONCLUSION 



In point of the positions which they hold on the shoot the two types of 

 spore-producing members, the sporangia and sporangiophores, show some 

 degree of uniformity : in either case the insertion may be directly upon 

 the axis or in the axil of the sporophyll, or they may be inserted further 

 outwards upon the surface of the sporophyll. Leaving for the moment 

 the Ferns on one side, illustrations may be taken from the strobiloid 

 types. As regards the simple sporangia, these may originate from the 

 axis quite apart from the subtending leaf, as in Selaginella (Fig. 360 A) : in 

 Lycopodium the sporangium arises from the upper surface of the leaf close to 

 its base (Fig. 360 B, c) ; but in Spejicerites it is borne at a point far removed 

 from the leaf-base, though otherwise in accordance with the Lycopod-type 

 (Fig. 360 D). Similarly with the sporangiophores, the insertion may be 



FIG. 360. 



Diagrams illustrating the varying positions respectively, of sporangia (upper row) and 

 of sporangiophores (lower row). It is seen that a parallelism exists. For details 

 see Text. 



on the axis or on the sporophyll, but they show rather more latitude of 

 detail : thus in Equisetum and in the ancient Archaeocalamites they are 

 seated upon the axis, showing no association with bract-leaves (Fig. 360 E) : 

 or in Calamostachys whorls of bracts may intervene between the successive 

 whorls of sporangiophores, but without individually subtending them (Fig. 

 360 F) : or the sporangiophore may, possibly by a secondary displacement, be 

 apparently axillary, as in Palaeostachya (Fig. 360 G) : or, again, the sporangio- 

 phore may arise from the upper surface of a sporophyll, in which case it 

 necessarily has a subtending position, as in the Psilotaceae (Fig. 3601): 

 a similar position is seen in Sphenophyllum majus (Fig. 360 H), but 

 in other species of the genus there are more complex arrangements 

 probably resulting from fission. 1 From such examples as these it appears 



1 Scott mentions a species (S. emarginatum) which appears to have borne its sporangio- 

 phores separately, so that they "have left their own distinct scars on the axis above 

 the bracteal node" (Progresstis, i. p. 153). This arrangement closely approaches that 

 of Palaeostachya, or of Calamostachys. 



